The present disclosure relates to systems and methods for compensation of skew between in-phase and quadrature signals in a fiber optic communications system.
Fiber optic channels in network communications systems are well known and are considered effective for data transmission, allowing relatively high bandwidth data communication. Optical fiber used in such channels is flexible and can be bundled as cables, and is generally considered to be advantageous for long-distance communications because light propagates through the fiber with little attenuation compared to electrical cables. Typical present day commercial optical fiber systems transmit data at 10 or 40 Gbit per second. Each fiber can carry multiple independent channels, each using a different wavelength of light in a technique known as wavelength-division multiplexing (WDM), thereby enhancing the net data rate of an optical fiber.
As more capacity is continually desired for networks, increased data transmission rates would be desirable. However, in fiber optic systems, as data rates increase various optical phenomena begin to manifest and act to limit data transmission rates. For example, a propagation skew between, for example, in-phase (I) and quadrature (Q) channels in a quadrature phase shift keyed (QPSK) system. Even relatively small amounts of skew between channels can begin to have a significant impact on system performance at increasing data rates. Such skew can result from, for example, slightly different length communications paths in a receiver, and/or thermal drift in a receiver.